So I use my phone as a metronome. I play a ticking clock MP3 on a loop. My entire workout sounds like being inside a mechanical clock.

Audio: Ticking clock

The sound is a familiar one from my childhood. I started taking piano lessons when I was 7, and a mechanical metronome accompanied my daily practice. But instead of struggling to keep up in tempo with a Bach suite, I sweat it out while trying to lift, breathe and count all at once.